This invention relates to an improved programming and control device for a modified lead ballast for HID lamps and particularly for HID sodium lamps.
The basic modifying device for a lead ballast is disclosed in the aforementioned application Ser. No. 282,993, filed July 14, 1981 by R. J. Spreadbury now abandoned. In its preferred form, a series-connected additional inductor and a gate-controlled AC switch are connected in parallel across the capacitor of the lead ballast and a sensing and programming means operates to sense at least one lamp operating parameter to control the proportion of time the AC switch is opened and closed, in order to vary the current input to the lamp. The programming and control device of the present application has been specifically tailored to operate with such a modifying apparatus for a lead-type ballast.
Electronic control of ballasted discharge lamps is well known and an early development in the field is U.S. Pat. No. 3,265,930 dated Aug. 9, 1966 to Powell wherein current is sensed to develop a signal which drives a switching means between a high impedance state and a low impedance state in order to control the power input to the discharge device. Another development is set forth in U.S. Pat. No. 3,344,310 dated Sept. 26, 1967 to Nuckolls wherein a variety of lamp operating parameters can be sensed in order to control the operation of the discharge lamp. These include a line current responsive control, a voltage responsive control, a light output responsive control and a lamp load current responsive control.
A further development is set forth in U.S. Pat. No. 3,590,316, dated June 29, 1971 to Engel et al. wherein an electronic wattmeter is utilized to measure the operating lamp wattage and this is converted into a phase controlled signal in order to maintain the lamp operating wattage at a predetermined value. Another system for controlling lamp wattage is disclosed in U.S. Pat. No. 4,162,429, dated July 24, 1979 to Elms et al. wherein lamp voltage and line voltage are sensed and these parameters are converted into separate current signals which are fed into a ramp capacitor to control the charging rate thereof. When the ramp capacitor achieves a predetermined level of charge during each half cycle of AC energizing potential, an AC switch is gated to shift the current level to the operating lamp, in order to control the wattage input thereto.
There are several different systems of multiplying electric signals and some of these are summarized in "Modern Techniques of Analog Multiplication", The Electronic Engineer, April 1970, pages 75-79, article by Cate. These multiplied signals can be used as part of an electronic wattmeter.
It is known to dim high-intensity-discharge lamps for the latter part of the night when less illumination is needed, in order to conserve energy, and such a system is disclosed in U.S. Pat. No. 4,292,570, dated Sept. 29, 1981 to Engel.